BACKGROUND: Extensive literature in human and animal models has documented an association between maternal smoking during pregnancy and externalizing behavior in offspring. It remains unclear; however, the extent to which postnatal environmental smoke exposure is associated with behavioral development, particularly for children whose mothers did not smoke during pregnancy. The present study examined whether magnitude of exposure to environmental smoke across the first four years of life demonstrated a linear association with later externalizing symptoms.
METHODS: Exposure was quantified through salivary cotinine measured when children were 6, 15, 24, and 48 months of age, providing a more accurate quantification of realized exposure than can be estimated from parental report of cigarettes smoked. Data were available for n = 1,096 (50% male; 44% African American) children recruited for the Family Life Project, a study of child development in areas of rural poverty.
RESULTS: Analyses indicate a linear association between cotinine and children's symptoms of hyperactivity and conduct problems. This association remained significant after controlling for family poverty level, parental education, parental history of ADHD, hostility, depression, caregiver IQ, and obstetric complications. Furthermore, this association was unchanged when excluding mothers who smoked during pregnancy from the model.
CONCLUSIONS: Findings are consistent with animal models demonstrating an effect of environmental exposure to nicotine on ongoing brain development in regions related to hyperactivity and impulsivity, and highlight the importance of mitigating children's exposure to environmental smoke, including sources that extend beyond the parents.